1. Field of the Invention
The present invention relates to a magnetic recording and reproduction apparatus, and more particularly to a magnetic recording and reproduction apparatus having means for evaluating the degree of data accuracy and means for detecting a fault to assure the quality of the apparatus.
2. Description of the Related Art
A magnetic recording and reproduction apparatus having a Viterbi detector is described in IEEE Transactions on Magnetics, Vol. 27, pp. 4538-4543.
This magnetic recording and reproduction apparatus is made up of a write precompensation circuit for correcting a bit shift which is generated at the time of reproduction, a low-pass filter for removing high-frequency noise components of an analog reproduction waveform signal read from a magnetic recording medium, an A/D converter for converting the analog reproduction waveform signal into a digital waveform signal, a waveform equalizer for shaping the digital waveform signal, and a Viterbi detector for identifying digital data from the shaped digital waveform signal. In this apparatus, a recording-reproduction signal processing circuit is contained in a one-chip LSI (Large Scale Integrated circuit) to meet requirements for reduction in size and increase in data transfer rate.
A criterion for deciding the quality of a magnetic recording and reproduction apparatus is the degree of data accuracy. The degree of data accuracy is dependent on the recording-reproduction channel parameters such as the amount of write precompensation of the write precompensation circuit, the cut-off frequency of the low-pass filter, and the equalization coefficient value of the waveform equalizer, as well as the electromagnetic conversion characteristics of a magnetic head and a magnetic medium. For producing a magnetic recording and reproduction apparatus of high quality, these parameters are required to be set to optimum values at the time of using the apparatus. In order to determine the optimum value of these parameters, on the other hand, the degree of data accuracy is required to be evaluated quantitatively at the time of parameter variations.
Generally, an error rate is used as a numerical value for quantifying the degree of data accuracy. When a magnetic recording and reproduction apparatus is being used under normal operating conditions, however, the error rate is so small that the measurement of the error rate requires a great amount of time, thereby making it difficult to decide the quality of the apparatus accurately.
JP-A-3-144969 discloses a technique in which the degree of data accuracy is evaluated by comparing the series of a digital waveform signal with the series of a reference signal, measuring the histogram of the resulted error value, and thus predicting the data error rate of the magnetic recording and reproduction apparatus.
On the other hand, as a conventional method of evaluating the degree of data accuracy, a level margin test is known. In the level margin test, a gate slice level to be compared with the amplitude of an output signal of the waveform equalizer is moved vertically, and by detecting missing bits or extra bits, the margin width of the gate slice level and the data error rate are measured.